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# Re: Asteroid echos on 2380 MHz

• Subject: [amsat-bb] Re: Asteroid echos on 2380 MHz
• From: Dan Schultz <n8fgv@xxxxxxxxx>
• Date: Fri, 16 Aug 2002 17:39:03 -0400

```A good source of information on the asteroid flyby is
http://skyandtelescope.com. The site includes finder charts.

Sky and Telescope reports the diameter as 500 meters (1/3 mile) and a
flyby distance of  527,000 kilometers (327,000 miles). Given that the
moon is 3475 kilometers (2159 miles) diameter at an average distance of
384,000 kilometers (239,000 miles), we can calculate as follows:

Size difference:
(500 meters) ^ 2 / (3475 km) ^ 2 = 48,302,500 times smaller projected
area than the moon
10*LOG (48,302,500) = 76.8 dB worse.

Range difference:
(527,000 kilometers) ^ 4 / (384,000 kilometers) ^ 4 = 3.55 times less
signal
10*LOG(3.5) = 5.5 dB worse.

Total: 82.3 dB worse.

Using your figures for Arecibo uplink power and antenna gain, the 80 dB
gain will just about offset the 82.3 dB loss due to the smaller size and
greater distance of the asteroid. It should be only 2.3 dB worse than a
100 watt amateur EME station. However I think most EME stations run more
than 100 watts, the asteroid reflection would be 12.3 dB worse than an
amateur EME station running 1 KW. So let's give it a listen and see if
you can hear it.

Dan Schultz N8FGV

>The asteroid is purportedly about 1/2 mile in diameter and passing at a

>distance of 300,000 miles (just beyond the orbit of the moon). So how
>strong an echo will this tiny rock produce compared to a moonbounce
signal
>(off a much bigger rock!)? Of course Arecibo will be running a signal
9000
>times as powerful as is used on 2304 MHz eme (avg 100w), and with 40 dB

>more antenna gain! That's about 80 dB stronger! the moon is about a
>quarter the size of the earth (guessing 2000 miles diameter) so that is

>(very) roughly (Drock)^2/ (Dmoon)^2 = 1/16,000,000 weaker reflection!

>So whatdya say? Is this possible?

>Ed, AL7EB

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